Computer systems, including servers and storage subsystems, use significant amounts of power. In the past, conserving power has always been secondary to speed and processor availability. However, Internet sites with excess capacity for high peak periods such as an Olympics website or an online stock trading website waste power keeping the computer systems ready for the next peak period. In addition, power problems and rolling blackouts, such as those experienced in California in 2000-2001 during deregulation, have begun to spur awareness that power conservation may be required in order to keep a network center operational. In addition, as microprocessors continue to scale up in speed and density, the microprocessor's power consumption will increase dramatically requiring more efficient power consumption.
Because of the increased processing demands required by today's software and Internet sites, more computer systems utilize multi-processor systems which require more power to operate than single processor computer systems. In multi-processor technology, multi-processor specifications describe how to start and stop processors in multi-processor servers. The multi-processor specifications select a boot processor and then add application processors as discovered, so that a multi-processor server is dynamically configured without a fixed foreknowledge of the number of processors in the server. But the multi-processor and the Advanced Configuration and Power Interface (“ACPI”) specifications do not typically allow for any power consumption control or savings from a source or decision engine external to the server unit in which the multiple processors reside nor do the specifications typically provide for strategic control over the multiple power supplies.
With the advent of power hungry processors and multi-processor computer systems, power management has become more important. The focus was first on portable computer systems to reduce power consumption as a means of maximizing battery life. From portables, the technology was applied to desktops, primarily to reduce the long boot time wait by leaving the machine in standby, rather than doing a cold boot each time. Specifically, Advanced Configuration and Power Interface (ACPI) in the Windows operating system addresses inclusion of ACPI power states in computer systems and allows the operating system to control the amount of power given to each device attached to a computer. For example, ACPI allows the operating system to turn off peripheral devices, such as a DVD-ROM player or a monitor, when the peripheral device is not in use. However, ACPI is a control method that is exercised by the operating system and is geared towards controlling the operation of peripheral devices and not the multi-processors. In many cases, the operating system on any specific machine does not have sufficient information to make knowledgeable decisions regarding the best enterprise level power management strategy for a server or rack of servers containing single or multi-processors. This decision must often be made outside the scope of the operating system running on any individual server for maximum utility, and further, the decision may not be based on the demand requirement for a particular server or processor.